The present variety ‘Hokuto Shiro Ichigoukin’ was produced using mutant fungal strains of two parent varieties, ‘Hokuto Hachigoukin’ (unpatented) and ‘Hokuto Jyunigoukin’ (unpatented), grown by Hokuto Sangyo Kabushiki Kaisha. Specifically, the + variety was ‘Hokuto Hachigoukin’ and the − variety was ‘Hokuto Jyunigoukin’. ‘Hokuto Hachigoukin’ and ‘Hokuto Jyunigoukin’ were each submitted to UV irradiation, and then the mutated varieties were crossbred to produce the present variety ‘Hokuto Shiro Ichigoukin’.
The site of development was on property of Hokuto Sangyo Kabushiki Kaisha Kinoko Sougo Kenkyusho in Nagano, Japan.
In April 2000, the mutated ‘Hokuto Hachigoukin’ was produced, in that a UV-irradiated strain was spawned on a culture medium. In August 2000, the mutated ‘Hokuto Hachigoukin’ was harvested, and monospores were isolated.
In parallel, in May 2000, the mutated ‘Hokuto Jyunigoukin’ was produced, also in that a UV-irradiated strain was spawned on a culture medium. In October 2000, the mutated ‘Hokuto Jyunigoukin’ was harvested, and monospores were isolated.
In September and October 2000, primary hyphae were obtained from mutated ‘Hokuto Hachigoukin’ and mutated ‘Hokuto Jyunigoukin’. From December 2000, mutated ‘Hokuto Hachigoukin’ and mutated ‘Hokuto Jyunigoukin’ were used to obtain crossbred stains. In February 2001, cultivation was started, and harvesting began in May 2001.
For cultivation, the cultivated hyphae are typically inoculated in a cultivation medium, like potato dextrose agar (PDA), filled in a sterilized cultivating dish for cultivation and subjected to treatment for growing the mushroom.
Further, in June 2001, a cultivation test was started for secondary selection. In October 2001, an HM222 strain, which appeared to be a superior variety, was selected. In December 2001, a cultivation test was initiated for stabilization.
In January 2002, a characteristic test was started. In May 2002, after repeated cultivation tests, stability, reproducibility and homogeneity, matching the objectives of improvements, were confirmed, i.e., the asexually propagated clones of the present plant are identical to the original plant in all distinguishing characteristics. Thus the HM222 strain was named ‘Hokuto Shiro Ichigoukin’.